Abstract 494: Identification and characterization of novel kinases that regulate BRCA1 expression and function

Abstract

Abstract Transcriptional and functional regulation of breast cancer susceptibility gene 1 (BRCA1) in the pathogenesis of sporadic breast cancers is poorly understood. About 90% of all breast cancers are considered sporadic, and 30-40% of these cases exhibit decreased expression of BRCA1 in the absence of mutations at its genetic locus. Loss of BRCA1 accelerates growth of tumor cells, while expression of BRCA1 leads to growth arrest and apoptosis. These observations support further examination of regulatory pathways of BRCA1 to restore its expression and function. To identify potential regulators of BRCA1, we developed a functional assay based on the role of BRCA1 in DNA damage repair. BRCA1 acts as a central scaffold that assembles a complex of repair proteins to sites of double-strand breaks (DSBs) following exposure to ionizing radiation (IR). Immunostaining for BRCA1 reveals these repair sites as punctate ionizing radiation-induced foci (IRIF). The ability of BRCA1 to localize to DSBs depends on both its expression and phosphorylation status. We evaluated the effect of siRNAs against kinases on BRCA1 IRIF formation because 1) phosphorylation of BRCA1 regulates many of its functions, 2) bioinformatics provides BRCA1 phosphorylation sites where the kinase involved is unknown, and 3) kinases play key roles in signaling pathways to influence gene expression or phosphorylation status. A number of kinases were identified that affected the ability of BRCA1 to form IRIF. However, the mechanism of kinase influence is unclear. Secondary siRNA screening assays have validated the kinase hits and lead kinases have been selected for further characterization. We are currently determining whether the effects of the lead kinases on BRCA1 are at the transcriptional or post-translational level and how these changes affect the ability of BRCA1 to repair DSBs by homologous recombination, to regulate the G2/M cell cycle checkpoint, and to modulate expression of downstream genes. Additionally, we are elucidating the signaling pathways that explain how the lead kinases regulate BRCA1. Once completed, we will have identified and characterized the role of the lead kinases on BRCA1 expression and function. This knowledge can translate into a novel therapy for BRCA1-related sporadic breast cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 494.